1. Field of the Invention
The present invention relates to an internal mold release agent for use in a reaction injection molding process for the preparation of optionally cellular, polyurea elastomer moldings.
2. Description of the Prior Art
Reaction injection molding processes for the production of optionally cellular polyurea elastomers have been described in U.S. Pat. Nos. 4,433,067, 4,444,910, 4,530,941 and 4,774,263. In addition, U.S. Pat. No. 4,396,729 discloses polysiloxane internal mold release agents for use in the production of polyurea elastomers. Finally, U.S. Pat. Nos. 4,519,965 and 4,581,386 are directed to the use of internal mold release agent mixtures for either polyurethane and/or polyurea elastomers which are based on a zinc carboxylate and a solubilizer to maintain the zinc carboxylate in solution in the isocyanate-reactive component used to prepare the elastomer.
One of the problems with this latter mold release agent mixture, especially in systems for the preparation of polyurea elastomers, is the difficulty of maintaining the zinc carboxylate in solution without precipitation. Further, parts prepared using the zinc carboxylate-based internal mold release agent mixture require special treatment after they are removed from the mold and before painting in order to remove excess mold release agent from the surface of the part to improve its paintability.
It is an object of the present invention to provide an internal mold release agent which does not suffer from the disadvantages of the prior art mold release agents when used for the production of polyurea elastomers. It has surprisingly been found that this object may be achieved in accordance with the present invention by using certain fatty acid polyesters described hereinafter as internal mold release agents in the production of optionally cellular, polyurea elastomers.
U.S. Pat. Nos. 4,201,847 and 4,254,228 both describe an internal mold release agent based on the reaction product of an organic polyisocyanate and a fatty acid ester for use primarily in the production of polyurethane elastomers. These references disclose that the fatty acid ester itself is not stable and forms an incompatible mixture with either the polyisocyanate or the polyol components used as starting materials. Accordingly, it is surprising that in accordance with the present invention these fatty acid esters remain stably dispersed in the isocyanate-reactive component used for the preparation of the polyurea elastomers.
U.S. Pat. No. 4,774,263 is directed to the production of polyurea elastomers using a mold release agent. This reference discloses that suitable mold release agents are the salts of fatty acids having at least 12 carbon atoms and either primary mono-, di- or polyamines containing 2 or more carbon atoms or amines containing amide or ester groups and having at least one primary, secondary or tertiary amino group according to U.S. Pat. No. 3,726,952; blends of two or more of the following in accordance with British Patent No. 1,365,215: (1) esters of monofunctional and/or polyfunctional carboxylic acids which contain --COOH and/or --OH groups and have OH or acid numbers of at least 5, (2) natural or synthetic oils, fats or waxes and (3) salts according to U.S. Pat. No. 3,726,952; salts of saturated or unsaturated aliphatic or cycloaliphatic carboxylic acids having at least 8 carbon atoms and tertiary amines which do not contain amide or ester groups in accordance with U.S. Pat. No. 4,098,731; and reaction products of ricinoleic acid and long chain fatty acids in accordance with U.S. Pat. No. 4,058,492.